1. Field of the Invention
The invention relates to a circuit testing apparatus, and more particularly to a circuit testing apparatus for measuring a differential output of a device under test.
2. Description of the Related Art
With the development of technology, integrated circuits (ICs) have become more powerful and important. In addition to integrated circuits processing specifically analog or digital signals, mixed-signal integrated circuits are being developed to process both analog and digital signals. Regardless of processing type, manufactures generally test each integrated circuit to ensure quality. Further, according to the integrated circuit test results, manufacturers determine whether the integrated circuit is qualified for distribution.
FIG. 1 is a diagram illustrating differential voltage output of an integrated circuit tested by a logic tester. As shown in FIG. 1, a common testing method used during mass production of an integrated circuit is exemplified. Generally, a logic tester 10 is used as a testing apparatus of the device under test 12 (for example, an integrated circuit) before leaving the factory. For convenience of testing, the device under test 12 is usually disposed on a device under test board 14. When the logic tester 10 measures a differential voltage of the device under test 12 with two output ends N1 and N2, a testing signal ST is provided for the device under test 12. Then a first output voltage from the first output end N1 of the device under test 12 corresponding to the testing signal ST is measured. Further a second output voltage from the second output end N2 of the device under test 12 corresponding to the testing signal ST is measured. Accordingly, the logic tester 10 obtains a differential output of the device under test 12 by performing a subtraction calculation, which subtracts the second output voltage VOUT− of the second output end N2 from the first output voltage VOUT+ of the first output end N1, so as to determine whether the device under test 12 has passed or failed the test with differential output. However, the above-mentioned testing method is performed by respectively measuring the first output voltage VOUT+ and the second output voltage VOUT− via the logic tester 10, thereby requiring a relatively lengthy testing time, thus decreasing integrated circuit testing efficiency.